In the related art, there is a known microscope in which evanescent illumination is used as a technique for observing a specimen in an extremely thin region in the immediate vicinity of the surface of a cover glass (for example, see Patent Literature 1).
Evanescent illumination is an illumination method in which laser light focused at a lens edge portion at a back focal position of a liquid-immersion objective lens is made incident on the liquid-immersion objective lens, and, by totally reflecting the laser light that has been converted to substantially collimated light by the liquid-immersion objective lens at the interface between the cover glass and the liquid, the evanescent light is made to leak out toward the cover glass. Although this is a general microscopy method that allows high-contrast observation of a specimen in an extremely thin region in the immediate vicinity of the surface of the cover glass, there is a problem in that total reflection illumination, with which illumination is provided from one direction, only allows biased fluorescence information to be obtained.
Therefore, there is a method in which shadow formation and speckle noise are suppressed in an image formed based on oblique illumination by acquiring a time-averaged image by rotating the direction in which laser light is made incident on the cover glass about the axis of the liquid-immersion objective lens (for example, see Patent Literature 2).
In the case in which the NA is increased for laser light that is made incident at the back focal position of the liquid-immersion objective lens in order to increase the viewing field area, the energy density of the laser light at this back focal position becomes extremely high, and the liquid-immersion objective lens is damaged by heat. Specifically, when the illumination region is increased by increasing the NA of the laser light, the diameter of a spot formed by the laser light at the back focal position is decreased, and, additionally, that the energy density of the laser light at the back focal position is increased accordingly because, in order to make the brightness of the larger illumination region equivalent to the brightness before increasing the size thereof, laser light to be made incident needs to have correspondingly higher energy. Furthermore, because it is necessary to perform time averaging, high-speed image acquisition is not possible, and thus, the imaging subject shifts due to vibrations of a galvanometer mirror, a motor, or the like.